Using goldfish in an avoidance-conditioning paradigm with shock as unconditioned and sound as conditioned stimulus, it is proposed to investigate why some animals fail to respond to operant conditioning by quantifying the modifiability of individual behavior. Considering behavior and its modification as Markov processes, behavior dynamcis are defined at three levels for individual subjects,for a set of mutually exclusive behaviors, as (1) a vector of existing state probabilities; (2) a state transition probability matrix, giving the probability that one behavior will give rise to another; and (3) for two successive training schedules, the matrix which transforms one state transition matrix into the succeeding one, thus giving the change in behavior "rules" as a result of change in the reinforcement rules. The various matrices will be tested for statistical equality, as tests of the hypothesis that there are (in respect to the type of matrix being tested) no significant inter-individual differences. Where significant differences are found, it will be attempted to relate these to the history of the individuals during the laboratory test and pre-test periods.